STOCKHOLM—Finland's Rovio Entertainment Ltd., maker of the blockbuster mobile game "Angry Birds," said Friday that Chief Executive Mikael Hed will step down in January—a surprise move that comes amid the company's struggles to refresh its games lineup and revenue model.

Mr. Hed will be succeeded by former Nokia Corp. executive Pekka Rantala, who joined Rovio earlier this year.

Rovio and its iconic Angry Birds game...

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